In German Pat. No. 2,327,230 there is disclosed a process for the selective hydrogenation of unsaturated hydrocarbons, particularly cyclopentadiene to form cyclopentene, whereby hydrogen is reacted with the unsaturated hydrocarbons in the presence of a catalyst containing an organic nickel derivative and a reducing agent characterized in that the reducing agent corresponds to the formula Al R.sub.1 R.sub.2 R.sub.3 or to the formula R-Li where R.sub.1, R.sub.2 and R.sub.3 are hydrogen or monovalent hydrocarbon radicals and R is a monovalent hydrocarbon radical and the operation is conducted in the presence of pyridine.
In this German patent it is said that maximum catalyst activity is advantageously produced by observing the following conditions. The mole ratio between the aluminum or lithium compound and the nickel salt can lie between 2.6/1 and 4/1 but normally a mole ratio of 3/1 is employed. The ratio between the pyridine and the nickel salt can lie between 1/1 and 2.5/1, but normally a ratio of 2/1 is employed. It is said that the temperature of catalyst preparation and the hydrogenation temperature can lie between 0 and 100.degree. C., but, generally, the catalyst is prepared between 10 and 50.degree. C. The hydrogenation generally takes place between 0 and 80.degree. C.
A number of examples are given in this German Patent. For instance, it is disclosed that into a reaction vessel, from which air and moisture have been removed, are introduced 300 milliliters (ml) of freshly prepared cyclopentadiene (CPD) and then the catalyst solution made by reacting 0.9 millimoles (mm) of triethylaluminum in benzene with a solution of 0.3 mm of nickel acetylacetonate in benzene which contains 0.6 mm of pyridine. The reaction is conducted at 30.degree. C. under hydrogen pressure of 30 bars. After a certain period of time, the reaction was stopped.
The applicant has set forth a number of experimental conditions, times and results of several of the experiments which were conducted and are reported in this German Patent. These experiments are set forth in the table below:
Table 1 ______________________________________ % % Ex Al/Ni Time Conv. of Cyclopentane Cyclopentene No Mole Ratio Min. CPD Obtained Obtained ______________________________________ 7 1.0 150 100 4 94 8 2.6 80 100 4 96 1 3.0 72 100 4 96 9 4.0 75 100 4 96 10 6.0 80 100 8 92 ______________________________________
What is particularly important here are the times employed in the hydrogenations of the table above. These times give an indication of the rate of the hydrogenations.